blind transfer causes phone to freeze

I have been trying to blind transfer between my two aastra 55i and 57i phones, and every time, the call transfers, but the phone that originally sent the transfer has to be restarted, it keep freezing. Is this an aastra problem or a 3cx?

You need to upgrade your firmware on these Aastra phones. It should solve your problem. I had the exact same issue and upgrading the firmware solved it. 888voipstore has a "how to" on the upgrade. The actual sip upgrade file can be gotten from the Aastra- North American terminals link, on the Aastra web site. After the upgrade, reset to factory defaults and reconfigure. It should work.